Compressed-air systems, in particular in utility vehicles, require a so-called compressed-air treatment installation, hereinafter also referred to as air treatment installation, downstream of the air compressor. In such treatment installations, the air is, inter alia, dried and filtered, and oil constituents are separated out. These processes all take place in a so-called drying agent cartridge which, broadly speaking, is composed of a base panel with openings for the throughflow of the air and of a cup-shaped or pot-shaped cover, which base panel and cover are fixedly connected to one another. In the drying agent cartridge there is situated a moisture-adsorbing granulate which extracts the moisture from the air flowing through. When used in a utility vehicle, the granulate has only a limited service life. A reason for this is that the oil mist contained in the compressed air is deposited on the granulate and thus reduces the effective surface area for the absorption of moisture. Furthermore, the granulate can mechanically break down as a result of the vibration loading. The drying agent cartridge must therefore be exchanged at regular intervals.
For this purpose, the cartridge is typically equipped with a female thread in the base panel. It is thus possible for the consumed cartridge to be unscrewed from, and for a new cartridge to be screwed onto, an external thread on the housing of the compressed-air treatment installation, for example on the air dryer housing. Use is normally made of a square-section sealing ring which is compressed axially as a result of the screw connection, thus imparts a sealing action, and at the same time ensures the axial bracing action of the screw connection. Drying agent cartridges of the type are known for example from the laid-open specifications DE 10 2013 103 066 A1, DE 10 2012 105 137 A1 and DE 10 2007 034 435 A1.
Depending on the installation location of the compressed-air treatment installation, the accessibility to the cartridge for an exchange is often restricted. The cartridge is always fastened to the top of the housing of the compressed-air treatment installation, and therefore the optimum direction of access for the exchange of the cartridge would be from above. This freedom however does not always exist owing to body structures in the case of heavy goods vehicles or generally in the case of buses. Furthermore, work is often performed from below if the vehicle is standing over the workshop pit.
Nowadays, in some cases very firmly seated cartridges exist, in the case of which the predefined service times for the cartridge exchange in the workshop cannot be adhered to. A very high release moment is required, which, despite auxiliary means such as for example a clamping strap with a long lever, is difficult to apply because the lateral free space for the use of a lever does not exist.
In the case of the fastenings between cartridge base panel and housing of the compressed-air treatment unit such as are known from practice, because the sealing element, typically a square-section sealing ring, must co-rotate during the screw connection process, large fluctuations arise in the tightening moment owing to different friction influences, and damage to or twisting of the sealing element occurs, which in turn results in leakage. Furthermore, the axial bracing action of the screw connection must be generated by way of the seal.